A drive transmission device that switches, when a rotation member on an input side and a rotation member on an output side are rotated relative to each other (that is, with a difference in a rotational speed), driving systems to be input to a planet gear mechanism has been employed in joint parts and the like of tools and robots.
For example, a drive transmission device disclosed in Japanese Unexamined Patent Application Publication No. 2013-133873 includes a clutch mechanism including a steel ball, a first rotary plate and a second rotary plate, the first rotary plate including a groove part which houses a part of the steel ball, the first rotary plate being coupled to an input axis, and the second rotary plate rotatably holding the steel ball and coupled to an output axis. The groove part of the first rotary plate includes a first cam surface and a second cam surface that are inclined with respect to the direction of the rotation axis. When a load is applied to the output axis and the first rotary plate and the second rotary plate are rotated relative to each other, the steel ball rolls on the first cam surface or the second cam surface of the first rotary plate, comes out of the groove part, and pushes the second rotary plate, whereby the driving systems to be input to the planet gear mechanism are automatically switched.